He has replaced David Beckham as Adidas's new poster boy. On the latest Adidas billboards, spread across London, he is sitting cross-legged; as if cooling his heals after a day's work out, peeping over Londoners, tired and overworked, telling them the secrets of his unfailing energy. Fauja Singh, Britain's most popular Sikh is 93, the oldest runner in Sunday's London Marathon. He is threatening to break his own world record of 5.40 hours in the 90 plus age bracket that he set last year. While running Marathon races in London, New York and Toronto last year, he raised thousands of pounds for various charities promoting Sikh culture around the world. He has also raised money for B.L.I.S.S., a charity dedicated to the care for premature babies. He describes it as the 'oldest running for the youngest'.

Fauja Singh shot to fame five years ago, when aged 89, he completed the gruelling 26.2 mile distance in 6 hours and 54 minutes. This knocked 58 minutes off the previous world best for anyone in the 90 plus age bracket. The career of this extraordinary Marathon runner is closely supervised by his personal trainer Harminder Singh. He says 'he can still run for a few more years. And perhaps in five years he might be the oldest man to run a Marathon.' Fauja Singh came to London in 1992 to live with his son after his wife's death in his village in Jalandhar. 'Sitting at home was really killing,' he says in Punjabi. 'Most elderly people in Britain eat a rich diet, don't move about and only travel in cars, and that makes them sick,' he says. He wasn't prepared to go the same way. So he took up jogging initially to beat the boredom of sitting at home.

'I never thought of running a Marathon then. But slowly it grew.' What surprises many is that he supports his eight stone and six feet tall body frame with a very simple vegetarian diet. 'I am very careful about different foods. My diet is simple phulka, dal, green vegetables, yoghurt and milk. I do not touch parathas, pakoras, rice or any other fried food. I take lots of water and tea with ginger.' And that smile is eternally fixed beneath his silver haired beard. Perhaps that's the reason behind his strikingly inspiring and positive attitude. 'I go to bed early taking the name of my Rabba [God] as I don't want all those negative thoughts crossing my mind.' Doesn't he find it difficult to cover 26 miles at this age? 'The first 20 miles are not difficult. As for last six miles, I run while talking to God.'

Last year, Adidas signed him up for its 'Nothing Is Impossible' advertising campaign. He won't reveal how much money the deal involves, but says that a large part of his earnings goes to charity.

But the question is how long can he continue to run Marathons. Steven Carroll, an expert in sports medicine says that Fauja Singh should go on running for as long as he likes, provided his cardiovascular system is able to support his gruelling schedule. But, he cautioned: 'No one should run a marathon, be they 16 or 93, without getting properly fit first. A marathon is a punishing event and anyone thinking of entering must build up endurance.' Last Friday, Fauja Singh had to go through his final medical test. 'They had all types of machines and took many tests. Everything is fine with me. Though my one leg is weaker than the other, I can complete the run,' he says wth a disarming smile. That's why the Adidas billboard warns the Marathon runners from Kenya: 'The Kenyans had better watch out for him when he hits 100.'